diff --git a/libexec/rc/rc.d/growfs b/libexec/rc/rc.d/growfs
index 5402bd442279..3c48a7dca6b2 100755
--- a/libexec/rc/rc.d/growfs
+++ b/libexec/rc/rc.d/growfs
@@ -1,144 +1,310 @@
 #!/bin/sh
 #
+# Copyright 2022 Michael J. Karels
 # Copyright 2014 John-Mark Gurney
 # All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions
 # are met:
 # 1. Redistributions of source code must retain the above copyright
 #    notice, this list of conditions and the following disclaimer.
 # 2. Redistributions in binary form must reproduce the above copyright
 #    notice, this list of conditions and the following disclaimer in the
 #    documentation and/or other materials provided with the distribution.
 #
 # THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 # ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 # IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 # ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 # FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 # DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 # OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 # HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 # LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 # OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 # SUCH DAMAGE.
 #
 # $FreeBSD$
 #
 
 # PROVIDE: growfs
 # REQUIRE: fsck
 # BEFORE: root
 # KEYWORD: firstboot
 
-# This allows us to distribute an image
-# and have it work on essentially any size drive.
+# Grow root partition to fill available space, optionally adding a swap
+# partition at the end.  This allows us to distribute an image and
+# have it work on essentially any size drive.
 
 # Note that this uses awk(1), and thus will not work if /usr is on a separate
 # filesystem.  We need to run early, because there might be not enough free
 # space on rootfs for the boot to succeed, and on images we ship - which are
 # the primary purpose of this script - there is no separate /usr anyway.
 
 . /etc/rc.subr
 
 name="growfs"
 desc="Grow root partition to fill device"
 start_cmd="growfs_start"
 stop_cmd=":"
 rcvar="growfs_enable"
 
-growfs_get_diskdev ()
+growfs_get_diskdev()
 {
 	local _search=${1}
 	sysctl -b kern.geom.conftxt |
 	while read x1 _type _dev line
 	do
 		if [ "${_type}" = "DISK" -a -n "$(echo ${_search} | grep ${_dev})" ]; then
 			echo -n ${_dev}
 			break
 		fi
 	done
 }
 
-growfs_start ()
+# Compute upper bound on swap partition size (if added), based on physmem
+# and vm.swap_maxpages / 2 (the limit that elicits a warning).
+# Rule for swap size based on memory size:
+#	up to 4 GB	twice memory size
+#	4 GB - 8 GB	8 GB
+#	over 8 GB	memory size
+growfs_swap_max()
 {
+	memsize=$(sysctl -n hw.physmem)
+	memsizeMB=$(($memsize / (1024 * 1024)))
+
+	if  [ $memsizeMB -lt 4096 ]
+	then
+		swapmax=$(($memsize * 2))
+	elif  [ $memsizeMB -lt 8192 ]
+	then
+		swapmax=$((8192 * 1024 * 1024))
+	else
+		swapmax=$memsize
+	fi
+
+	pagesize=$(sysctl -n hw.pagesize)
+	vm_swap_max=$(($(sysctl -n vm.swap_maxpages) / 2 * $pagesize))
+
+	if [ $swapmax -gt $vm_swap_max ]
+	then
+		$swapmax=$vm_swap_max
+	fi
+	echo -n "$swapmax"
+}
+
+# Find newly-added swap partition on parent device ($1).
+growfs_last_swap()
+{
+	swapdev=$(gpart list $1 | awk '
+		$2 == "Name:" { dev = $3 }
+		$1 == "type:" && $2 == "freebsd-swap" { swapdev = dev }
+		END { print swapdev }
+	    ')
+	echo -n $swapdev
+}
+
+growfs_start()
+{
+	verbose=0
 	echo "Growing root partition to fill device"
 	FSTYPE=$(mount -p | awk '{ if ( $2 == "/") { print $3 }}')
 	FSDEV=$(mount -p | awk '{ if ( $2 == "/") { print $1 }}')
 	case "$FSTYPE" in
 	ufs)
 		rootdev=${FSDEV#/dev/}
 		;;
 	zfs)
 		pool=${FSDEV%%/*}
 		rootdev=$(zpool list -v $pool | awk 'END { print $1 }')
 		;;
 	*)
 		echo "Don't know how to grow root filesystem type: $FSTYPE"
 		return
 	esac
 	if [ x"$rootdev" = x"${rootdev%/*}" ]; then
 		# raw device
 		rawdev="$rootdev"
 	else
 		rawdev=$(glabel status | awk -v rootdev=$rootdev 'index(rootdev, $1) { print $3; }')
 		if [ x"$rawdev" = x"" ]; then
 			echo "Can't figure out device for: $rootdev"
 			return
 		fi
 	fi
 
 	if [ x"diskid" = x"${rootdev%/*}" ]; then
 		search=$rootdev
 	else
 		search=$rawdev
 	fi
 
 	diskdev=$(growfs_get_diskdev ${search})
 	if [ -z "${diskdev}" ]; then
 		diskdev=${rootdev}
 	fi
 
+	# Check kenv for growfs_swap_size; if not present,
+	# check $growfs_swap_size from /etc/rc.conf.
+	# A value of 0 suppresses swap addition,
+	# "" (or unset) specifies the default;
+	# other values indicate the size in bytes.
+	# If default, check whether swap is already in fstab;
+	# if so, don't add another.
+	addswap=1
+	swapsize="$(kenv -q growfs_swap_size 2>/dev/null)"
+	case "$swapsize" in
+	"0")	addswap=0
+		;;
+	"")	case "$growfs_swap_size" in
+		"0")	addswap=0
+			;;
+		"")
+			if ! awk '
+				/^#/ { next }
+				$3 == "swap" { exit 1 }
+			    ' < /etc/fstab
+			then
+				addswap=0
+			fi
+			;;
+		*)	swapsize="$growfs_swap_size"
+			;;
+		esac
+		;;
+	*)	;;
+	esac
+
+	swaplim=$(growfs_swap_max)
+
+	[ $verbose -eq 1 ] && {
+		echo "diskdev is $diskdev"
+		echo "search is $search"
+		echo "swapsize is $swapsize"
+		echo "swaplim is $swaplim"
+	}
+
 	sysctl -b kern.geom.conftxt | awk '
 {
+	verbose = 0
 	lvl=$1
 	device[lvl] = $3
 	type[lvl] = $2
 	idx[lvl] = $7
+	offset[lvl] = $9
 	parttype[lvl] = $13
+	size[lvl] = $4
+	if (verbose) print lvl, type[lvl], $3
+	if (type[lvl] == "DISK") {
+		disksize = size[lvl]
+		if (verbose)
+			print "disksize ", disksize
+		# Don't add swap on disks under 15 GB (decimal) by default.
+		if (addswap == 1 && (size[lvl] > 15000000000 || swapsize > 0))
+			doing_swap = 1
+		else
+			doing_swap = 0
+	} else if (type[lvl] == "PART" && $11 == "freebsd-swap" && \
+	    int(swapsize) == 0) {
+		# This finds swap only if it precedes root, e.g. preceding disk.
+		addswap = 0
+		doing_swap = 0
+		print "swap device exists, not adding swap"
+	}
 	if (dev == $3) {
 		for (i = 1; i <= lvl; i++) {
 			# resize
 			if (type[i] == "PART") {
 				pdev = device[i - 1]
-				cmd[i] = "gpart resize -i " idx[i] " " pdev
+				if (verbose)
+					print i, pdev, addswap, disksize, \
+					    doing_swap
+				swapcmd = ""
+				# Allow swap if current root is < 40% of disk.
+				if (parttype[i] != "MBR" && doing_swap == 1 && \
+				    (size[i] / disksize < 0.4 || \
+				    swapsize > 0)) {
+					print "Adding swap partition"
+					if (int(swapsize) == 0) {
+						swapsize = int(disksize / 10)
+						if (swapsize > swaplim)
+							swapsize = swaplim
+					}
+					sector = $5
+					swapsize /= sector
+					if (verbose)
+						print "swapsize sectors",
+						    swapsize
+					align = 4 * 1024 * 1024 / sector
+
+					# Estimate offset for swap; let
+					# gpart compute actual start and size.
+					# Assume expansion all goes into this
+					# partition for MBR case.
+					if (parttype[i - 1] == "MBR") {
+					    if (verbose)
+						print "sz ", size[i - 1], \
+						    " off ", offset[i - 1]
+					    expand = size[0] - \
+						(size[i - 1] + offset[i - 1])
+					} else {
+					    if (verbose)
+						print "sz ", size[i], \
+						    " off ", offset[i]
+					    expand = size[0] - \
+						(size[i] + offset[i])
+					}
+					if (verbose)
+					    print "expand ", expand, \
+						" sz ", size[i]
+					swapbase = (expand + size[i]) / sector
+					swapbase -= swapsize + align
+					swapcmd = "gpart add -t freebsd-swap -a " align " -b " swapbase " " pdev "; kenv growfs_swap_pdev=" pdev " >/dev/null; "
+					if (verbose)
+						swapcmd = "set -x; " swapcmd
+				}
+				cmd[i] = swapcmd "gpart resize -i " idx[i] " " pdev
 				if (parttype[i] == "GPT")
 					cmd[i] = "gpart recover " pdev " ; " cmd[i]
 			} else if (type[i] == "LABEL") {
 				continue
 			} else {
 				print "unhandled type: " type[i]
 				exit 1
 			}
 		}
 		for (i = 1; i <= lvl; i++) {
 			if (cmd[i])
 				system(cmd[i])
 		}
 		exit 0
 	}
-}' dev="$search"
+}' dev="$search" addswap="$addswap" swapsize="$swapsize" swaplim="$swaplim"
 	gpart commit "$diskdev" 2> /dev/null
 	case "$FSTYPE" in
 	ufs)
 		growfs -y /dev/"$rootdev"
 		;;
 	zfs)
 		zpool online -e $pool $rootdev
 		;;
 	esac
+
+	# Get parent device of swap partition if one was added;
+	# if so, find swap device and label it.
+	pdev=$(kenv -q growfs_swap_pdev)
+	if [ -n "$pdev" ]
+	then
+		dev=$(growfs_last_swap "$pdev")
+		if [ -z "$dev" ]
+		then
+			echo "Swap partition not found on $pdev"
+			exit 0
+		fi
+		glabel label -v growfs_swap $dev
+	fi
 }
 
 load_rc_config $name
 run_rc_command "$1"